Tribological Properties of Friction Pairs in Lubricant Contaminated with Particles under High Temperature

A liquid–solid lubricant with sand particles of different sizes and concentrations is prepared in advance. The viscosity of the lubricant is measured by a capillary viscometer to determine its relationship to the concentration or size of the sand particles. The relationships between friction and concentration or size of the sand particles are also identified with a UMT2 tribometer. Results indicate that the size of sand particles plays an important role in the lubrication performance; when the size of sand particles is 1–5 μm, the friction coefficient of the liquid–solid lubricant is reduced at low concentration and low load. Contaminant concentration greatly influences the tribological behavior of such a lubricant. The failure probability of the part surface decreases with a reduction in particle concentration; moreover, a high temperature aggravates the friction and wear of this surface. The friction coefficient is 0.14 at 200°C, which is well above the friction coefficient at room temperature (0.078), and the wear volume also increases by 30% compared to the normal temperature. When the temperature is 300°C the wear volume is two times that under room temperature.     

Demonstrating Improved Fuel Economy Using Subsystem Specific Lubricants on a Modified Diesel Engine

Fuel economy performance in modern internal combustion engines is of increasing importance to lubricant formulators due to regulations targeting global greenhouse gas emissions. Engines typically employ a single lubricant, with a common sump, to service all components. As a result, base oil and additive selection for fuel economy performance is a compromise among competing demands for different engine subsystems. Opportunities for significant fuel economy improvement through targeted formulation of lubricants for specific engine subsystems are presented, with specific emphasis on segregating the lubricant supplies for the valve train and the power cylinder subsystems. A working prototype was developed in a lab environment by modifying a commercially available twin-cylinder diesel engine. Motored valve train and whole-engine fired test results were obtained and compared to model data. Fuel economy benefits were demonstrated using market representative heavy-duty diesel lubricants, including mineral oil and polyalphaolefin (PAO) blends. The fuel economy benefits of a dual-loop lubricant system are demonstrated through significant viscosity reduction in the power cylinder subsystem, achieving overall engine friction reductions of up to 8% for the investigated operating condition. Results suggest that additional gains may be realized through targeted base oil and additive formulation. Implications for incorporation in larger diesel engines are also considered.     

Scuffing Resistance and Starved Lubrication Behavior in Helicopter Gear Contacts: Dependence on Material,Surface Finish,and Novel Lubricants

A loss of lubrication event within rotorcraft drivetrain components leads to the rapid failure of contacting gear and bearing surfaces, thermal runaway, and catastrophic damage with possible loss of life. This article demonstrates that the scuffing failure of the gear and bearing surfaces can be delayed by varying the properties of the contact materials and residual lubricant in high-speed contacts. A ball-on-disc tribometer is used to simulate loss of lubrication conditions in gears for a variety of material, surface finish, and lubricant combinations to compare relative time to scuffing initiation at high entrainment and sliding velocities (both 16 m/s). Comparisons of material and surface finishing generally show that contacts tend to survive longer without lubricant if the coefficient of friction is relatively low during initial run-in. However, a 9 cSt oil produced longer times to failure than the baseline 5 cSt oil with higher coefficients of friction throughout the experiment. Further measurements showed that silicon nitride and AISI 9310 steel in contact can survive much longer after the lubricant supply is shut off compared to a steel-on-steel contact. The 9 cSt oil, silicon nitride, and superfinished surfaces showed the greatest promise in loss of lubrication technology from these results, with increases of 28, 388, and 1,538%, respectively, over baseline results. Thus, material, surface finish, and novel lubricant selection strategies may allow tailoring of survivability characteristics of aircraft mechanical systems.     

Grinding performance improvement of silicon nitride ceramics by utilizing nanofluids

Silicon nitride ceramics are widely used as advanced structural components because of their excellent thermal and mechanical properties at ambient and elevated temperatures. In manufacturing industries, grinding is an efficient and productive technique for finishing ceramic workpieces. However, high wheel-workpiece friction and the extreme hardness associated with silicon nitride cause large heat generation during grinding. The heat produced during grinding impairs the workpiece quality by inducing surface and sub-surface damages, tensile residual stresses etc. The damages can critically limit the applications of ground ceramic components. Extensive experimental studies have been carried out to find the effect of dry and nano MQL (Graphite, WS₂ and MoS₂) grinding conditions on silicon nitride using resin bonded diamond wheel at different parametric (wheel speed, depth of cut and table speed) combinations. Results indicate that the use of nanofluids considerably improve the process performance in terms of grinding forces, surface finish and sub-surface damage. The ground surface is characterized by optical microscopy, SEM/EDX and XRD.     

Tribological,Mechanical Properties,and Morphology of Polyphenylene Oxide/Ultrahigh Molecular Weight Polyethylene Blends

Ultrahigh molecular weight polyethylene-g-polystyrene was synthesized as a compatibilizer through a suspension-grafting copolymerization method. Various weight ratios of polyphenylene oxide/ultrahigh molecular weight polyethylene-g-polystyrene/ultrahigh molecular weight polyethylene blends were prepared by extruding, and mechanical properties, morphology as well as tribological behavior were investigated. Tensile strength, flexural strength, and Rockwell hardness increased with the increasing of the compatibilizer. Impact strength and antiwear properties of the blends were improved significantly by contrast to those of pure polyphenylene oxide. The polyphenylene oxide/ultrahigh molecular weight polyethylene-g-polystyrene/ultrahigh molecular weight polyethylene blend of 90/10/0 compared with other ratios as an optimum ratio. In this case, the wear volume and friction coefficient of the blend were 2.6% of PPO and 45% lower than PPO, respectively.     

考虑空化效应的微孔端面机械密封泄漏量计算及机理的研究

微孔端面机械密封泄漏量的数值计算方法和机理都不明确。基于质量守恒的JFO空化边界条件建立了微孔端面机械密封的数值计算模型。数值计算结果表明沿着泄漏方向的不同截面的流量并不相等,所以必须要选择合理的积分截面才能计算出正确的泄漏量。根据径向流量场、周向流量场和压力场的分析,讨论了沿着泄漏方向流量不等的原因,揭示了空化效应和动压效应形成高压区,造成泄漏方向流体沿周向运动,从而降低了泄漏量。最后给出了微孔端面机械密封泄漏量计算的公式和方法。     

材料填充对开槽轴承接触力与润滑性能的影响

轴承滚道界面的润滑状态及接触力对轴承寿命的影响十分显著,为提高圆柱滚子轴承寿命,提出了在轴承外圈开槽填充弹性体的方法。采用有限元法计算了不同槽宽及丁晴橡胶、尼龙1010、硬铝合金和紫铜四种填充材料对轴承内滚道和滚子接触力的影响。在此基础上,建立了考虑圆柱滚子轴承真实表面粗糙度混合润滑数学模型,分析了不同转速下不同填充材料对轴承润滑性能的影响。结果表明：轴承外圈开槽并填充弹性体对轴承的润滑状态和接触力影响显著;最大受载滚子与内滚道的接触力随着填充材料弹性模量的减小而减小,采用丁晴橡胶和尼龙1010填充材料可明显增加滚子接触个数,有效降低接触力。转速的增加会使油膜变厚、摩擦系数、接触载荷比、接触面积比、最大接触应力减小,采用丁晴橡胶填充材料轴承润滑性能最好。     

微量润滑喷嘴电晕电极的电场特性及其对油雾荷电性能的影响研究

针对静电气雾微量润滑系统的电晕电极产生的高压静电场影响润滑油雾的荷电性能,以及电晕电极的结构形式决定了电场的强度和分布的问题,对不同电晕电极数量及布置型式对空间电场强度的影响展开了分析。利用Ansoft Maxwell软件对不同结构形式电晕电极的空间电场强度进行了仿真,并建立了电晕静电气雾微量润滑油雾荷电性能测试系统,研究了不同电极结构形式对油雾荷质比的影响。研究结果表明,对比多电晕电极,单电晕电极具有结构简单、电场强度高以及高场强集中分布于润滑油锥状气雾区域的特点。电晕电极的空间电场仿真结果与油雾荷质比实验结果基本符合,单电晕电极的油雾荷质比优于多电晕电极,适用于电晕静电气雾微量润滑系统。     

水泥磨主轴承的润滑及其管理

球磨机是水泥生产工艺流程中很重要的一种粉碎设备,其正常运转率下的运行是保证水泥厂效益的一个重要因素。主轴承作为球磨机的一个重要部件,其润滑管理尤其重要。作者试图结合自己多年的工作心得,并从技术维护的角度分析Φ2.2m×6.5m水泥磨主轴承的润滑管理。     

WZT-1000D新型卧式振动离心脱水机的技术创新和应用效果

介绍了WZT-1000D新型卧式振动离心脱水机的工作原理及在线性惯性振动排料系统、双电机驱动强迫同步振动器激振、筛篮主轴系结构优化、独立的油腔浸油润滑等多方面的创新技术;现场的应用结果表明,该设备的脱水工艺指标先进,脱水后的产品水分低,设备的可靠性高。